Why Did My Plywood Supplier Go Ballistic on Me??

Discussion in 'Materials' started by CatBuilder, May 6, 2010.

  1. CatBuilder

    CatBuilder Previous Member

    I have shopped my order to 2 different suppliers for the 45' cat I'm building.

    The second supplier, seeing that I needed 160 sheets of 3mm Luan ply nearly jumped through the phone and smacked me!

    He said, "I'd never put my family and friends or risk my life on a boat where the hull was constructed of Luan plywood!" "That stuff isn't marine grade!" "It's made with glue that isn't waterproof!"

    I guess I'm lost here because the other supplier just gave me the quote for the ply, no questions asked.

    I'm building using the Cylinder Mold (<---this is a link) method advocated by Kurt Hughes.

    The method calls for using 3mm Luan to make the hulls (vacuum bagged on a mold).

    Why is someone telling me now that a boat made of Luan would be a deathtrap?? :confused:

    How could so many of Kurt's boats be in charter service as "inspected vessels" (more than 6 passengers, inspected annually by the US Coast Guard) if they are somehow unsafe?

    I'm really lost here... can anyone figure out what the supplier is talking about? :confused:

    Is there anything wrong with a Luan hull constructed of two layers of 3mm Luan ply, scarfed bonded and bagged, then glassed outside, 6 layers of epoxy outside and 3 layers of epoxy inside?
  2. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form

    Not all luan plywood is marine grade. Maybe you were not specific enough about the grade you needed or he misunderstood what you were asking for. Some luan plywood is rated for interior application only and will delaminate with even one exposure to moisture.
  3. duluthboats
    Joined: Mar 2002
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    duluthboats Senior Dreamer

    I think in your case the ply is just core material and should be fine if that is what Kurt has designed for.
  4. alan white
    Joined: Mar 2007
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    alan white Senior Member

    Ask for sample from each supplier and do a boil test.
  5. CatBuilder

    CatBuilder Previous Member

    I guess that's probably it. Thanks for the advice. The designer (Kurt) suggested the boil test as well no matter what I use.

    I guess I just have to be more specific. I am looking for low cost plywood with waterproof glue and thick/even face layers?

    This is my first boat that involves wood and I keep thinking I'm missing something.
  6. Stumble
    Joined: Oct 2008
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    Stumble Senior Member


    I think what you are missing is that there is no such animal as cheap Marine grade anything. Marine grade means a couple of things but most importantly

    1) No voids in the interior wood. This is critical if you are doing any bending or shaping of the wood as it prevents soft and hard spots.

    2) minimal knots in the plys. See reason for 1

    3) Waterproof glue

    4) limited types of woods that have some natural protection from water

    None of this is cheap, and while you can build a boat out of anything it won't last if you do.
  7. CatBuilder

    CatBuilder Previous Member

    I'd like my boat to last the rest of my wife's life and she just turned 30, so I do want to use the best of everything.

    So... what 3mm ply that can easily bend should I be using? Okoume?

    I should point out that I've been playing with (owning boats) since 1992 or so and have owned one every year ever since then, totaling 4 boats. This new cat is my 5th. I've also done marine repairs as a small business. We have worked chartering and living aboard since the early 2000's. I'm on land for the first time since then right now to build this boat. I've been first mate aboard a megayacht and have a USCG 100T Masters. All of my boats and all the boats I've worked on have been fiberglass - either balsa core or just glass, so I'm a newbie when it comes to understanding marine plywood.

    Not trying to be a jerk, but letting the board know that while I'm new at building a boat, I've got some "on the water" and repair experience.

    I'm sharing my background because I think it might help people to know where to pitch the response. To allow people to just spout off anything at any technical boat level (but at a beginner woodworking level).

    So... I know nothing marine is cheap. But, Kurt's literature always talks about using doorskins and Luan and how inexpensive it is. It appears to me that this was the case a while back, but is now less the case.

    I think maybe you used to be able to find cheap luan plywood that was void free and didn't delaminate in the boiling water test. Now however... as my plywood supplier said, that is maybe not the case?

    Do I go with Okoume? Meranti? Is there something else I should consider?

    I want a first quality boat that will last my wife's lifetime (another 50-60 years??). I don't want to make any mistakes on the construction of the boat, which is why I'm all ears on what it is I should be using for longevity.

    Thank for the responses so far. Keep 'em coming! And hope I didn't sound like a jerk listing off my marine credentials. Just wanted to make sure you all know where I come from so I can get straight talk answers. :)

    I want to get this right for sure, but I'm basically clueless on wood. Even though I've done some fiberglass repair work, I'm brand new to wood composite boats. Make sense?
  8. apex1

    apex1 Guest

    If I may step in here?

    Go here:


    click "marine plywood"
    lookup the different types and properties
    Okoume is the cheapest there (and in general the lightest).

    Do not skimp on the ply, Lauan and doorskin is crap! It does not last the building time, let alone the launching...........

    And, btw. reconsidering the design / designer would be a second thought!!!
    Our member Masalai is building to a different method with another designer, and although I personally do´nt like the method too much (nor do I like multihulls), I must say, that his boat seems to come out worth the investment.

    We have seen quite a few "El Cheapo extremo" "Designers" here and elsewhere. I, personally would not let my enemy go to sea in their boats!


    ahhh. and go back to that "non" supplier when you buy your wood! He is a honest man!
  9. CatBuilder

    CatBuilder Previous Member

    I know... that "non" supplier has just won all my business because he was very honest and took a lot of time to correct me.

    Thank you for stepping in. I could use all the help I can get with wood. :confused: :(

    You suggested changing designers. I have seen several of these boats from Kurt out there since the mid 1980's doing charters every day - 25 years of chartering and they are still working. One sistership called Zeevonk was built in the Netherlands and is currently doing charters in the Caribbean.

    Here are some links to his boats:





    http://www.kamanu.com/ (this is a 1984 Hughes still chartering)

    .... and a quote from Kurt's marketing material, "Cylinder Molded multihulls have come a long way in the last twenty six years. By now in 2009 there are hundreds of CM built multis out there building or sailing now. The original KAMANU, the first C.M. USCG certified charter catamaran has been sailing nonstop for nearly twenty five years. Dozens of C.M. cats are now USCG certified to carry passengers. Builders on all continents are finding out that Cylinder Molding can give them the very highest quality wood/epoxy multi hulls in less time than any other one-off construction system there is. "

    Sure, like all marketing, it's a little bit over the top, but they seem to be holding up over the years and holding up in value. These are the facts I based my designer choice on.

    I'm not going to defend the designer here, but I would like to understand what you see as wrong with this build method.

    What are some of the weaknesses? What problems do you see, other than "it's a catamaran?" :p

    Again, not trying to disprove, but trying to learn. Those facts are the ones I used to decide. Are there other facts only experienced builders would know that I'm missing?:?:
  10. CatBuilder

    CatBuilder Previous Member

    BTW: Very good link for learning the various grades of plywood. Thank you. Looks like Okoume it is!
  11. apex1

    apex1 Guest

    Do´nt get me wrong,

    the method (I have no experience with) might be worth every effort. The designer definetively not!

    the difference in cost between doorskin and highest grade marine ply is less than nothing, compared with the overall investment!!!!

    So, how can one seriously promote such crap for building a structure you cross the 7 seas in?
    Thats a IDIOT..........no matter how nice, valuable, or successful his designs may be.

    if the initial statement was true....................

    From the page provided above, I could extract some reasonable comments proving the guy knows what he is talking, and there has´nt been a doorskin recommendation.
    Quote>>>>CM hulls are better suited for some types of multis than others. I see CM as being ideal for hulls such as tri amas or charter cats where interior living in the hull is not needed. I see CM as having the least advantage in hulls such as livaboard cats where interior is everywhere in the hull and the structure must be carefully finished.


    Finally, one must be careful about which plywood to use. Some types of excellent plywood might be too stiff to compound. With the great number of useful plywoods out there, that does not need to be a problem.<<<Quote end.

    There was no doorskin mentioned..........


    btw. I am building in wood epoxy since Hannibal crossed the Alpine Mountains.
  12. Charly
    Joined: Dec 2009
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    Charly Senior Member

    Hi Apex,
    I have enjoyed reading your responses here, and am learning a lot. I also appreciate Catbuilder asking so many questions-- so that I don't have to:)

    I have crossed the Rubicon already with Kurt Hughes Designs. I have purchased the plans and some materials, and have e-mailed back and forth with Kurt over a few issues, while his responses have been rather, well, curt:) they have always been prompt and informative. I see him as a dedicated sort of person, with a lot of stuff going on, and only so much time in the day to work with, So far, I am more than satisfied... Having said that, if you have issues with any of his designs, or anything else, I would like to know, since I respect your opinion, and am about to start building his 36 Daycharter Cat. Thanks!

  13. Charly
    Joined: Dec 2009
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    Charly Senior Member

    Hey Catbuilder,

    Fwiw, I my experience with Boulter has been good. I think the only 3mm they have in stock now is okume. the website says that their 3mm stuff is made to BS 6566, but mine came stamped 1088. Not sure what That means. It is nice stuff though.

  14. apex1

    apex1 Guest

  15. captainmorgan
    Joined: May 2010
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    Location: Baja Mexico

    captainmorgan New Member

    Your Boat is cold molded plasticized

    Basically you are building a plastic boat.

    You can use that plywood because of the amount of glass and the amount of layers you are putting on.

    The strength in your boat will come from the glass and not the plywood.

    As far as the Coast Guard and insurance companies are concerned you are not going to have a problem and it will be insured as a glassboat not a wood boat. Insurance companies are moving away from wood boats because of fire retardant issues. ie glass doesn't burn as quickly.
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